Process for producing thermoelectric semiconductor alloy, thermoelectric conversion module, thermoelectric power generating device, rare earth alloy, producing process thereof, thermoelectric conversion material, and thermoelectric conversion system using filled skutterudite based alloy

ABSTRACT

A process for producing a rare earth alloy comprises heating a raw material alloy to be a molten alloy, and quench-solidifying the molten alloy, wherein the raw material alloy is compounded so as to have a composition represented by the formula: RE x (Co 1-y M y ) 4 Sb 12  (wherein RE is at least either one member of La and Ce, M is at least one member selected from the group consisting of Ti, Zr, Sn, Cu, Zn, Mn and Pb, 0&lt;x≦1, and 0&lt;y&lt;1).

CROSS-REFERENCE

This is a divisional application of U.S. patent application Ser. No.11/583,100, filed Oct. 19, 2006, which is a continuation ofPCT/JP2005/008103 filed Apr. 21, 2005, the disclosure of which isincorporated by reference, and priority is claimed on Japanese PatentApplication No. 2004-374218, filed Dec. 24, 2004, Japanese PatentApplication No. 2004-246830, filed Aug. 26, 2004, Japanese PatentApplication No. 2004-236712, filed Aug. 16, 2004, Japanese PatentApplication No. 2004-125153, filed Apr. 21, 2004, and domestic benefitis claimed from U.S. Provisional Patent Application No. 60/565,521 filedApr. 27, 2004, U.S. Provisional Patent Application No. 60/603,268 filedAug. 23, 2004, U.S. Provisional Patent Application No. 60/607,345 filedSep. 7, 2004, and U.S. Provisional Patent Application No. 60/640,242filed Jan. 3, 2005. The contents of each of the four Japanese PatentApplications for which priority is claimed and the contents of each ofthe four U.S. Provisional Patent Applications for which domestic benefitis claimed are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a production method of a thermoelectricsemiconductor alloy, and a high-performance thermoelectric powergenerating device using a thermoelectric semiconductor alloy produced bythe production method.

The present invention relates to rare earth alloys suitable for athermoelectric conversion element of directly converting heat intoelectricity by the Seebeck effect.

The present invention relates to a device and a method for generatingthermoelectric power by utilizing a thermoelectric conversion element.More specifically, the present invention relates to a thermoelectricconversion system using a filled skutterudite-based alloy for thethermoelectric conversion element of directly converting heat intoelectricity by the Seebeck effect.

BACKGROUND ART

To cope with the regulation for emission of carbonic acid gas and energyconservation, thermoelectric power generation utilizing thermoelectricconversion of converting waste heat directly into electricity isattracting attention. This thermoelectric conversion is effected by sucha mechanism that when temperature difference is generated by assigningone end of n-type and p-type semiconductors to a high temperature andanother end to a low temperature, potential difference is caused andelectricity is obtained. The principle thereof has long been known.

For example, JP-A-2001-189495 (the term “JP-A” as used herein means an“unexamined published Japanese patent application”), WO03/019681 A1,JP-A-2004-253618, JP-A-2004-119647, Yamanaka et al., Kinzoku (Metals),Vol. 74 (8), page 54 (2004), Matsuura et al., Journal of Japan Instituteof Metals, Vol. 66 (7), page 767 (2002), and S. Shuto et al., Proc. 22ndInternational Conference on Thermoelectrics, 312 (2003) disclose varioustypes of thermoelectric conversion material.

Conventional thermoelectric power generation had been used only forlimited uses such as application to space probe, because thesemiconductor used for the power generation is very expensive, but inthe late 1990s, a high-performance semiconductor was newly discoveredand since then, aggressive development such as study on materials forpractical use, production of modules and packaging test has been made.

Examples of the substance taken notice of as a next-generationthermoelectric semiconductor include filled skutterudite type, cobaltoxide, silicide and Heusler type. It is recognized that with thesematerials, high electric conductivity, high Seebeck coefficient and lowthermal conductivity can be achieved at the same time. For enhancing theperformance of each material, a great deal of effort is being made.

Along with elucidation of properties as a semiconductor, alloys having aHeusler or half Heusler structure have come to draw attention as anexcellent thermoelectric semiconductor. The Heusler alloy is representedby the formula: A_(3-X)B_(X)C, wherein A and B are each a transitionmetal, C is a Group III or IV metal, and a space group is Fm3m. The halfHeusler alloy is represented by the formula: ABC, wherein A and B areeach a transition metal, C is a Group III or IV metal, and the spacegroup is F43m.

In the case of using a Heusler alloy as a thermoelectric semiconductor,the design is difficult due to numerous combinations of elements, andone proposed guideline therefor is a method of using an electronicnumber as a rough standard.

With respect to the thermoelectric semiconductor having a Heuslerstructure, for example, Nishino et al. have reported an Fe₂VAl system ofgiving an output factor comparable to that of Bi—Te system in thevicinity of room temperature. The Fe₂VAl system is expected in view ofthe theoretical value to exhibit thermoelectric performance higher thanthe Bi—Te system and also from the aspect of expensiveness or toxicity,is noteworthy as a practical material.

At present, for the production of a half Heusler alloy as athermoelectric conductor for use in middle and high temperature regions,a heat treatment for a long time of about 10 days is performed.Considering mass production, the heat treatment for such a long time isnot preferred because this causes increase in the cost.

Also, it is known that in the TiNiSn system having a half Heuslerstructure, when Ti is replaced by Zr or Hr, both high output factor andlow thermal conductivity can be achieved in a high temperature region of300° C. or more and the dimensionless figure of merit ZT as a roughstandard for the performance of a practical material exceeds 1.0 at693K. The performance of this system is expected to be enhanced infuture.

When a Heusler alloy is produced by casting, high melting point metalssuch as Ti, V and Zr are contained therein in many cases and a skilledtechnique is required for the quench-solidification of high-temperaturemolten metal. Also, a casting technique in vacuum induction furnace andinert atmosphere is necessary because of handling of a readilyoxidizable metal as represented by Ti.

DISCLOSURE OF INVENTION

In most of conventional methods for producing a thermoelectricsemiconductor, the alloy raw material is melted by arc melting, andannealing of the molten alloy for a long time is performed multipletimes or a shaped body is produced at high temperature under highpressure by using a special heat shaping apparatus. Thus, theproductivity is not taken account of at all.

In the light of these problems, an object in the present inventionin thepresent invention is to provide a high-performance thermoelectricconversion module, a high-performance thermoelectric power generatingdevice, and a thermoelectric semiconductor alloy for constituting such amodule or device.

Out of intermetallic compounds such as CoSb₃ having a skutterudite-typecrystal structure, which are one conventional thermoelectric conversionmaterial, the thermoelectric conversion material having a filledskutterudite structure is low in the thermal conductivity and therefore,promising as a thermoelectric conversion material for use particularlyin high-temperature regions.

The filled skutterudite-based alloy is an intermetallic compoundrepresented by the formula: RT₄Pn₁₂ (wherein R is a rare earth metal, Tis a transition metal, and Pn is an element such as P, As or Sb), wherean atom with a large mass, such as rare earth metal (R), is filled in apart of interstitial present in a crystal having a skutteruditestructure represented by the formula: TPn₃ (wherein T is a transitionmetal, and Pn is an element such as P, As and Sb).

The filled skutterudite-type thermoelectric conversion material can beproduced as either p-type or n-type by appropriately selecting thetransition metal T. Moreover, this material has no anisotropy andtherefore, the crystal need not be oriented, so that the productionprocess can be simple and easy and excellent productivity can beensured.

The p-type and n-type filled skutterudite-type thermoelectric conversionelements each in the block form are electrically joined directly orthrough a metal conductor to create p-n junction, or thermoelectricconversion materials comprising p-type and n-type filledskutterudite-based alloys, respectively, are contacted in a horseshoeshape to create p-n junction, whereby a module of thermoelectricconversion elements can be produced. Furthermore, when a plurality ofthermoelectric conversion elements having p-n junction are connected anda heat exchanger is joined therewith, a thermoelectric conversion systemis established and electricity can be taken out by the effect oftemperature difference.

The thermoelectric figure of merit ZT of the thermoelectric conversionelement can be expressed by:

ZT=α ² T/κρ

wherein α is Seebeck coefficient, ρ is electrical resistivity, κ isthermal conductivity and T is absolute temperature.

As seen from this formula, in order to enhance the performance of thethermoelectric conversion element, it is demanded to elevate the Seebeckcoefficient and reduce the electrical resistivity and thermalconductivity.

However, as known from the Wiedemann-Franz law, these elevation andreduction are theoretically difficult when the thermal conduction isgoverned by electronic conduction.

On the other hand, in the case of filled skutterudite, it is recognizedthat when a rare earth metal atom is filled in interstitial of a crystalhaving a skutterudite structure, the rare earth metal atom vibrates dueto weak bonding to Sb, and phonon scattering dominated by this vibrationoccurs, as a result, the thermal conductivity decreases.

Also, the filled skutterudite expresses an apparently large effectivemass ascribable to the heavy fermion-like behavior resulting fromcontaining a rare earth element and therefore, it is expected that bothreduction of electrical resistance and elevation of Seebeck coefficientcan be realized at the same time by doping or substituting a specificelement.

For example, in JP-A-11-135840, specifically, for improving the elementperformance, in the case of an n-type filled skutterudite element, atechnique of replacing Co on the transition metal site of YbCo₄Sb₁₂ byPt or replacing Ce on the rare earth metal site of CeFeCo₃Sb₁₂ by Zr orBa, thereby enhancing the properties has been reported. In the case of ap-type filled skutterudite element, it is known that when Fe on thetransition metal site of YbFe₄Sb₁₂ is replaced by Ni, the performance isenhanced.

In order to spread a thermoelectric conversion system, the properties ofthe thermoelectric conversion element must be enhanced withoutincreasing the raw material cost, but metals used in conventionalmethods all are expensive or require care in the handling. Therefore,enhancement of properties by using more inexpensive and easilyhandleable elements is demanded.

In most of conventional production methods, powders are mixed to give apredetermined composition and plasma-sintered, but this is unsuitablefor industrial mass production and moreover, replacement of a specificsite by the uniform addition of a trace element is difficult.

By taking account of these problems, an object in the present inventionis to provide novel rare earth alloys using easily available rawmaterials, being suitable for mass production and ensuring sufficientlyhigh performance as a thermoelectric conversion element.

The thermoelectric conversion material comprising a filledskutterudite-based alloy is low in the thermal conductivity as comparedwith intermetallic compounds such as CoSb₃ having a skutterudite-typecrystal structure, which are one conventional thermoelectric conversionmaterial, and therefore, this material is promising as a thermoelectricconversion material for use particularly in high-temperature regions.

The filled skutterudite-based alloy is an intermetallic compoundrepresented by the formula: RT₄Pn₁₂ (wherein R is a rare earth metal, Tis a transition metal, and Pn is an element such as P, As or Sb), wherean atom with a large mass, such as rare earth metal (R), is filled in apart of interstitial present in a crystal having a skutteruditestructure represented by the formula: TPn₃ (wherein T is a transitionmetal, and Pn is an element such as P, As and Sb). It is recognized thatwhen a rare earth metal atom is filled in interstitial of a crystalhaving a skutterudite structure, the rare earth metal atom vibrates dueto weak bonding to Pn, and phonon scattering dominated by this vibrationoccurs, as a result, the thermal conductivity of the thermoelectricconversion material comprising a filled skutterudite-based alloydecreases.

It is also recognized that the filled skutterudite-based alloy can beproduced as either p-type or n-type by appropriately selecting R or T.For the purpose of controlling the p-type or n-type, attempts are beingmade to replace a part of the T component comprising Fe by Co, Ni or thelike.

The p-type and n-type filled skutterudite-based alloy blocks produced inthis way are joined directly or through a metal conductor to create p-njunction, whereby a thermoelectric conversion element can be produced.Also, thermoelectric conversion materials comprising p-type and n-typefilled skutterudite-based alloys, respectively, are contacted in ahorseshoe shape to create p-n junction, whereby a module ofthermoelectric conversion elements can be produced.

Furthermore, when a plurality of thermoelectric conversion elementshaving p-n junction are connected and a heat exchanger is joinedtherewith, a thermoelectric conversion system is established andelectricity can be taken out by the effect of temperature difference.

Conventionally, for producing a thermoelectric conversion element byusing a filled skutterudite-based alloy, high-purity powdered rawmaterials such as rare earth metal, transition metal and P, As or Sb areweighed to give an objective filled skutterudite alloy composition andmixed, the mixture is once calcined at a temperature of 800° C. or less,the calcined product is again ground and then heated to 800° C. by hotpressing or plasma discharge sintering to produce a sintered body, andthe sintered body is cut to obtain the element.

However, in this method, the crystal grain diameter of the filledskutterudite-based alloy is greatly affected by the state of powderedraw materials. Also, unless the sintering conditions are strictlycontrolled, the crystal grain diameter grows large and the performanceof the thermoelectric conversion element disadvantageously decreases.

For example, in JP-A-2000-252526, for the purpose of solving theseproblems, as concerns an Sb-containing skutterudite-type thermoelectricmaterial which is one of filled skutterudite-type thermoelectricconversion materials, a technique of constituting the sintered body frompulverized crystal grains having a skutterudite structure and at thesame time, dispersing a metal oxide in the grain boundary of the crystalgrain has been proposed.

According to this method, the crystal grain having a skutteruditestructure can have an average crystal grain diameter of 20 μm or less.However, this method has a problem that due to interposition of a metaloxide in the crystal grain boundary, the electric conductivitydecreases.

As another method of producing a thermoelectric conversion materialcomprising a filled skutterudite-based alloy, for example, inJP-A-2002-26400, a method of heat-treating a ribbon produced by a liquidquenching process is known. In the general liquid quenching process,while rotating a roll at a high speed, a molten metal is poured thereonunder pressure through a nozzle produced by punching a hole of about 1mm at the distal end of a quartz-made tube.

However, in this method, the ribbon is amorphous or contains adecomposition product such as Sb₂Fe and Sb and therefore, a filledskutterudite element having a sufficiently high purity can be hardlyobtained. Also, for realizing use in practice, heat treatment at 873 to1,073K for 5 hours or more must be performed.

Furthermore, these methods described above all have a problem that whenthe process from the preparation of raw materials until sintering isperformed in an atmosphere allowing for the presence of oxygen, such asair, the rare earth metal element in the filled skutterudite structurecrystal is eliminated from the lattice and a part of the filledskutterudite structure is decomposed into Sb₂Fe and Sb.

In the present invention, the filled skutterudite-based alloy isproduced by a strip casting method, whereby the problems in conventionalmethods of producing a filled skutterudite-type thermoelectricconversion material can be overcome. That is, the present inventionprovides a method for producing a filled skutterudite-based alloy usableas-is for a thermoelectric conversion element, and an alloy produced bythe method, which can be suitably used for thermoelectric conversionelements.

Furthermore, the present invention provides a thermoelectric conversionmodule greatly elevated in the thermal conversion efficiency byproducing the thermal conversion element from an alloy comprising only afilled skutterudite phase.

The present inventors have found that when a raw material alloy ismelted and the molten alloy is quench-solidified at an appropriatecooling rate, a thermoelectric semiconductor alloy comprising nearly asingle phase can be produced.

The present invention has been accomplished based on this finding andincludes the following inventions.

-   (1) A process for producing a skutterudite compound comprising:-   heating a raw material alloy to obtain a molten alloy, and-   quench-solidifying a molten alloy at a cooling rate of 1×10² to    1×10³° C./sec.-   (2) A process for producing a skutterudite compound as set forth in    (1), in which the skutterudite compound is a filled skutterudite    compound.-   (3) A process for producing a Heusler type alloy including:-   heating a raw material alloy to obtain a molten alloy, and-   quench-solidifying a molten alloy at a cooling rate of 1×10² to    1×10³° C./sec.-   (4) A process for producing a Heusler type alloy as set forth in    (3), in which the Heusler type alloy contains a Heusler phase.-   (5) A process for producing a Heusler type alloy as set forth in (3)    or (4), inwhich the Heusler type alloy contains a half Heusler    phase.-   (6) A process for producing a Heusler type alloy as set forth in any    one of (3) to (5), in which the Heusler type alloy contains a    Heusler phase by not less than 90%.-   (7) A process for producing a Heusler type alloy as set forth in any    one of (3) to (6), in which the Heusler type alloy contains a    different type element by not less than 0.01 mass % in the Heusler    phase.-   (8) A process for producing a rare earth alloy including:-   heating a raw material alloy to be a molten alloy, and-   quench-solidifying the molten alloy.-   (9) A process for producing a rare earth alloy as set forth in (8),    in which the quench-solidifying is performed at a rate not lower    than 1×10²° C./sec.-   (10) A process for producing a rare earth alloy as set forth in (8),    in which the quench-solidifying is performed at a rate of 1×10² to    1×10³° C./sec.-   (11) A process for producing a rare earth alloy as set forth in (8),    in which the quench-solidifying during 1500 to 1700° C. is performed    at a rate of 1×10² to 1×10³° C./sec.-   (12) A process for producing a rare earth alloy as set forth in (8),    in which the quench-solidifying is performed by a strip casting    method.-   (13) A process for producing a rare earth alloy as set forth in (8),    in which the rare earth alloy is one selected from the group    consisting of a Heusler alloy, a half Heusler alloy, and a    skutterudite alloy.-   (1-1) A process for producing a Heusler alloy, including    quench-solidifying a molten alloy at a cooling rate of 1×10² to    1×10³° C./sec to produce a Heusler alloy represented by the formula:    A_(3-X)B_(X)C (wherein A and B each is at least one member selected    from transition metals consisting of Fe, Co, Ni, Ti, V, Cr, Zr, Hf,    Nb, Mo, Ta and W, and C is at least one member selected from Group    13 or 14 elements consisting of Al, Ga, In, Si, Ge and Sn).-   (1-2) A process for producing a Heusler alloy, including    quench-solidifying a molten alloy at a cooling rate of 1×10² to    1×10³° C./sec to produce a Heusler alloy represented by the formula:    ABC (wherein A and B each is at least one member selected from    transition metals consisting of Fe, Co, Ni, Ti, V, Cr, Zr, Hf, Nb,    Mo, Ta and W, and C is at least one member selected from Group 13 or    14 elements consisting of Al, Ga, In, Si, Ge and Sn).-   (1-3) An alloy produced by the production method described in (1-1)    or (1-2).-   (1-4) The alloy as described in (1-3), in which the ratio of    strongest peak of the Heusler phase or half Heusler phase is 85% or    more.-   (1-5) The alloy as described in (1-3) or (1-4), in which the average    particle diameter is from 1 to 100 μm.-   (1-6) A thermoelectric conversion element using the alloy described    in any one of (1-3) to (1-5).-   (1-7) A thermoelectric conversion module using the thermoelectric    conversion element described in (1-6).-   (1-8) A thermoelectric power generating device using the    thermoelectric conversion module described in (1-7).-   (1-9) A waste heat recovery system using the thermoelectric power    generating device described in (1-8).-   (1-10) A solar heat utilizing system using the thermoelectric power    generating device described in (1-8).

The present inventors have found that when a raw material alloy ismelted and solidified at an appropriate cooling rate, a filledskutterudite alloy comprising a skutterudite phase nearly as a singlephase can be produced. When the process in the present inventionin thepresent invention is employed, replacement of a specific site even by atrace element can be performed uniformly in the entire alloy and this issuited for mass production. However, depending on the alloy composition,the element fails in having sufficiently high performance.

As a result of investigations to elevate the element performance in thisproduction process, the present inventors have found that when in ann-type filled skutterudite thermoelectric conversion materialrepresented by RE_(x)(Co_(1-y)M_(y))₄Sb₁₂, RE is Ce or La, x is 0<x≦1,preferably 0.01≦x≦1, and Co is replaced by at least one member Mselected from Cu, Mn and Zn, which are relatively easily available andeasily handleable, in the range of 0<y<1, preferably 0.01≦y≦0.15, thethermoelectric conversion property can be enhanced.

It has been also found that when in a p-type filled skutteruditethermoelectric conversion material represented byRE_(x)(Fe_(1-y)M_(y))₄Sb₁₂ not using Co at all, the rare earth elementRE is Ce or La, x is 0<x≦1, preferably from 0.01 to 1, and Fe isreplaced by at least one member M selected from Ti, Zr, Sn and Pb in therange of 0<y<1, preferably 0.01≦y≦0.15, the thermoelectric conversionproperty can be enhanced.

The second aspect of the present invention includes the following modes.

-   (2-1) A rare earth alloy represented by RE_(x)(Fe_(1-y)M_(y))₄Sb₁₂    (wherein RE is at least either one member of La and Ce, M is at    least one member selected from the group consisting of Ti, Zr, Sn    and Pb, 0<x≦1, and 0<y<1).-   (2-2) The rare earth alloy as described in (1) above, in which x is    in the range of 0.01≦x≦1 and y is in the range of 0.01≦y≦0.15.-   (2-3) The rare earth alloy as described in (2-1) or (2-2) above, in    which the crystal structure is a skutterudite-type crystal    structure.-   (2-4) The rare earth alloy as described in (2-1) or (2-2) above, in    which the crystal structure is a filled skutterudite-type crystal    structure.-   (2-5) The rare earth alloy as described in any one of (2-1) to    (2-4), in which the average thickness of the rare earth alloy is    from 0.1 to 2 mm.-   (2-6) A p-type thermoelectric conversion material comprising the    rare earth alloy described in any one of (2-1) to (2-5) above.-   (2-7) A rare earth alloy represented by RE_(x)(Co_(1-y)M_(y))₄Sb₁₂    (wherein RE is at least either one member of La and Ce, M is at    least one member selected from the group consisting of Ti, Zr, Sn    and Pb, 0<x≦1 and 0<y<1).-   (2-8) The rare earth alloy as described in (2-7) above, in which x    is in the range of 0.01≦x≦1 and y is in the range of 0.01≦y≦0.15.-   (2-9) The rare earth alloy as described in (2-7) or (2-8) above, in    which the crystal structure is a skutterudite-type crystal    structure.-   (2-10) The rare earth alloy as described in (2-7) or (2-8) above, in    which the crystal structure is a filled skutterudite-type crystal    structure.-   (2-11) The rare earth alloy as described in any one of (2-7) to    (2-10), in which the average thickness of the rare earth alloy is    from 0.1 to 2 mm.-   (2-12) An n-type thermoelectric conversion material comprising the    rare earth alloy described in any one of (2-7) to (2-11) above-   (2-13) A process for producing a rare earth alloy, including    weighing raw materials to give a composition of    RE_(x)(Fe_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member    of La and Ce, M is at least one member selected from the group    consisting of Ti, Zr, Sn and Pb, 0<x≦1, and 0<y<1), melting the raw    materials in an inert gas atmosphere, and then quench-solidifying    the melt.-   (2-14) The process for producing a rare earth alloy as described in    (2-13) above, in which the quench-solidification is performed by a    strip casting method.-   (2-15) The process for producing a rare earth alloy as described in    (2-13) or (2-14), in which the cooling rate at the    quench-solidification is 1×10²° C./sec or more.-   (2-16) A process for producing a rare earth alloy, including    weighing raw materials to give a composition of    RE_(x)(Co_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member    of La and Ce, M is at least one member selected from the group    consisting of Ti, Zr, Sn and Pb, 0<x≦1, and 0<y<1), melting the raw    materials in an inert gas atmosphere, and then quench-solidifying    the melt.-   (2-17) The process for producing a rare earth alloy as described in    (2-16) above, in which the quench-solidification is performed by a    strip casting method.-   (2-18) The process for producing a rare earth alloy as described in    (2-16) or (2-17), in which the cooling rate at the    quench-solidification is 1×10²° C./sec or more.-   (2-19) A thermoelectric conversion element comprising a combination    of a rare earth alloy described in at least one of (2-1) to (2-4)    above and a rare earth alloy described in at least one of (2-7) to    (2-10) above.-   (2-20) A thermoelectric conversion module using the thermoelectric    conversion element described in (2-19) above.-   (2-21) A thermoelectric power generating device using the    thermoelectric conversion module described in (2-19) above.-   (2-22) A thermoelectric power generating method using the    thermoelectric conversion module described in (2-19) above.-   (2-23) A waste heat recovery system using the thermoelectric power    generating device described in (2-21) above.-   (2-24) A solar heat utilizing system using the thermoelectric power    generating device described in (2-21) above.

The present invention includes the following inventions.

-   (3-1) A thermoelectric conversion module using a filled    skutterudite-based alloy produced by melting an alloy raw material    comprising a rare earth metal R (wherein R is at least one member    selected from La, Ce, Pr, Nd, Sm, Eu and Yb), a transition metal T    (wherein T is at least one member selected from Fe, Co, Ni, Os, Ru,    Pd, Pt and Ag) and a metal antimony (Sb), and quench-solidifying the    molten metal by a strip casting method.-   (3-2) A thermoelectric power generating device using the    thermoelectric conversion module described in (3-1).-   (3-3) A thermoelectric power generating method using the    thermoelectric conversion module described in (3-1).-   (3-4) A waste heat recovery system using the thermoelectric power    generating device described in (3-2).-   (3-5) A solar heat utilizing system using the thermoelectric power    generating device described in (3-2).

The present inventors have found that when a raw material alloy ismelted and solidified at an appropriate cooling rate, a filledskutterudite alloy comprising a skutterudite phase nearly as a singlephase can be produced.

When the method in the present invention is employed, replacement of aspecific site even by a trace element can be performed uniformly in theentire alloy and this is suited for mass production. However, dependingon the alloy composition, the element fails in having sufficiently highperformance.

As a result of investigations to elevate the element performance in thisproduction method, the present inventors have found that when in ann-type filled skutterudite thermoelectric conversion materialrepresented by Ce(Co_(1-x)M_(x))₄Sb₁₂, CO is replaced by at least onemember M selected from Cu, Mn and Zn, which are relatively easilyavailable and easily handleable, preferably in the range of x from 0.01to 0.15, the thermoelectric conversion property can be enhanced.

It has been also found that when in a p-type filled skutteruditethermoelectric conversion material represented by La(Fe_(1-x)M_(x))₄Sb₁₂not using Co at all, Fe is replaced by at least one member M selectedfrom Ti, Zr, Sn and Pb, preferably in the range of x from 0.01 to 0.15,the thermoelectric conversion property can be enhanced.

The present invention has been accomplished based on these findings andincludes the following modes.

-   (4-1) A rare earth element-containing alloy represented by    La(Fe_(1-x)M_(x))₄Sb₁₂ (wherein M is at least one member selected    from the group consisting of Ti, Zr, Sn and Pb, and 0<x<1).-   (4-2) The rare earth element-containing alloy as described in (4-1)    above, wherein x is in the range of 0.01 to 0.15.-   (4-3) The rare earth element-containing alloy as described in (4-1)    or (4-2) above, wherein the crystal structure is a skutterudite-type    crystal structure.-   (4-4) The rare earth element-containing alloy as described in (4-1)    or (4-2) above, wherein the crystal structure is a filled    skutterudite-type crystal structure.-   (4-5) A p-type thermoelectric conversion material comprising the    rare earth element-containing alloy described in any one of (4-1) to    (4-4) above.-   (4-6) A rare earth element-containing alloy represented by    Ce(Co_(1-x)M_(x))₄Sb₁₂ (wherein M is at least one member selected    from the group consisting of Cu, Zn and Mn, and 0<x<1).-   (4-7) The rare earth element-containing alloy as described in (4-6)    above, in which x is in the range of 0.01 to 0.15.-   (4-8) The rare earth element-containing alloy as described in (4-6)    or (4-7) above, in which the crystal structure is a    skutterudite-type crystal structure.-   (4-9) The rare earth element-containing alloy as described in (4-6)    or (4-7) above, wherein the crystal structure is a filled    skutterudite-type crystal structure.-   (4-10) An n-type thermoelectric conversion material comprising the    rare earth element-containing alloy described in any one of (4-6) to    (4-9) above-   (4-11) A method for producing a rare earth element-containing alloy,    comprising weighing raw materials to give a composition of    La(Fe_(1-x)M_(x))₄Sb₁₂ (wherein M is at least one member selected    from the group consisting of Ti, Zr, Sn and Pb, and 0<x<l), melting    the raw materials in an inert gas atmosphere, and then    quench-solidifying the melt.-   (4-12) The method for producing a rare earth element-containing    alloy as described in (4-11) above, in which the    quench-solidification is performed by a strip casting method.-   (4-13) The method for producing a rare earth element-containing    alloy as described in (4-11) or (4-12), in which the cooling rate    from 1,500° C. to 700° C. at the quench-solidification is from 10²    to 10³° C./sec.-   (4-14) A process for producing a rare earth element-containing    alloy, including weighing raw materials to give a composition of    Ce(Co_(1-x)M_(x))₄Sb₁₂ (wherein M is at least one member selected    from the group consisting of Cu, Zn and Mn), melting the raw    materials in an inert gas atmosphere, and then quench-solidifying    the melt.-   (4-15) The process for producing a rare earth element-containing    alloy as described in (4-14) above, in which the    quench-solidification is performed by a strip casting method.-   (4-16) The method for producing a rare earth element-containing    alloy as described in (4-14) or (4-15), in which the cooling rate    from 1,500° C. to 700° C. at the quench-solidification is from 10²    to 10³° C./sec.-   (4-17) A thermoelectric conversion element comprising a combination    of a rare earth element-containing alloy described in any one of    (4-1) to (4-5) above and a rare earth element-containing alloy    described in any one of (4-6) to (4-10) above.

According to the first aspect in the present invention, a thermoelectricconversion module and a thermoelectric power generating device eachexhibiting high performance over a wide temperature range from a lowtemperature near room temperature to a high temperature region of 700°C. or more can be provided at a low cost. Also, a production method of aHeusler alloy or half Heusler alloy for the production of such a moduleor device can be provided.

According to the first aspect of the present invention, a trace elementcan be uniformly doped in the entire alloy or can be made to replace aspecific site in the crystal structure, whereby replacement of aspecific site is facilitated, for example, the V or Al site of Fe2VAlmay be partially replaced by Ti or Si, respectively, or Ti or Sn ofTiNiSn may be partially replaced by Zr or Sb, respectively.

According to the second aspect in the present invention, ahigh-efficiency thermoelectric conversion material can be produced at alow cost on an industrial scale, and a thermoelectric conversion elementof practical level can be provided.

More specifically, according to the present invention, a nearly uniformfilled skutterudite-based alloy can be easily and simply produced in alarge amount by casting using a strip casting method.

The present invention is not only high in the industrial utility valuedue to use of La or Ce having little restraint in resources out of rareearth metals, but also effective in lightening the environmental loadbecause of no use of Pb (lead), Te (tellurium) or the like. Also, thefilled skutterudite-based alloy in the present invention exerts highperformance in a high-temperature region of 300° C. or more andtherefore, the power output is large. In addition, a quench-castingmethod capable of continuous production is employed and combined with apressing-sintering technique, so that the element can be produced froman alloy comprising only a filled skutterudite phase which is ahigh-performance component, as a result, performance equal to or greaterthan that of conventional Pb—Te type elements can be achieved and both ahigh Seebeck coefficient and a low electrical resistance can berealized. Furthermore, by virtue of low thermal conductivity, thethermoelectric conversion module can be made compact.

The thermoelectric conversion module as a preferred embodiment in thepresent invention can be used in a high-temperature region up to 700° C.and therefore, when integrated into a waste heat utilizing system, thequantity of heat recovered by the heat exchanger can be increased and inturn, the quantity of unused heat can be decreased. That is, heatdiscarded so as to lower the operation temperature can be decreased andtherefore, great elevation of the thermal conversion efficiency andremarkable increase of the power output can be realized.

Also, when integrated into a cogeneration system, unused heat(unnecessary warm water) can be converted into electricity and thisleads to enhanced fuel efficiency and increased power output, so thatthe thermoelectric conversion module in the present invention cancontribute to the elevation of power generation efficiency as a centerpart of a thermoelectric power generating module.

The high-performance thermoelectric element produced by the presentinvention can contribute to the elevation of power generation efficiencyas a center part of a thermoelectric power generating module ofconverting heat into electricity by using, as the heat source, not onlywaste heat on a large scale including those in various industrialfurnaces and incinerators but also unused waste heat on a small scalesuch as exhaust gas from various cogenerations, water heaters andautomobiles, and natural energy (e.g., ground heat, solar heat), andthis is a very effective measure against global warming.

According to the third aspect in the present invention, a nearly uniformfilled skutterudite-based alloy can be easily and simply produced in alarge amount by casting using a strip casting method. The filledskutterudite-based alloy produced by the production method in thepresent invention can be used as-is for a thermoelectric conversionelement without passing through grinding and sintering steps andtherefore, the production cost of the thermoelectric conversion elementcan be greatly decreased.

The present invention is not only high in the industrial utility valuedue to use of La having little restraint in resources out of rare earthmetals but also effective in lightening the environmental load becauseof use of a metal free from a harmful substance (Pb (lead), Te(tellurium)) or the like. Also, the filled skutterudite-based alloy inthe present invention exerts high performance in a high-temperatureregion of 300° C. or more and therefore, the power output is large. Inaddition, a quench-casting method capable of continuous production isemployed and combined with a pressing-sintering technique, so that theelement can be produced from an alloy comprising only a filledskutterudite phase which is a high-performance component, as a result,performance equal to or greater than that of conventional Pb—Te typeelements can be achieved and both a high Seebeck coefficient and a lowelectrical resistance can be realized. Furthermore, by virtue of lowthermal conductivity, the thermoelectric conversion module can be madecompact.

The thermoelectric conversion module as a preferred embodiment in thepresent invention can be used in a high-temperature region up to 700° C.and therefore, when integrated into a waste heat utilizing system, thequantity of heat recovered by the heat exchanger can be increased and inturn, the quantity of unused heat can be decreased. That is, heatdiscarded so as to lower the operation temperature can be decreased andtherefore, great elevation of the thermal conversion efficiency andremarkable increase of the power output can be realized.

Also, when integrated into a cogeneration system, unused heat(unnecessary warm water) can be converted into electricity and thisleads to enhanced fuel efficiency and increased power output, so thatthe thermoelectric conversion module in the present invention cancontribute to the elevation of power generation efficiency as a centerpart of a thermoelectric power generating module.

A production process established in the production of rare earthsintered magnets is employed, so that mass production at a low cost inan industrial scale can be facilitated as compared with conventionalbatch-type production systems.

The high-performance thermoelectric element produced by the presentinvention can contribute to the elevation of power generation efficiencyas a center part of a thermoelectric power generating module ofconverting heat into electricity by using, as the heat source, not onlywaste heat on a large scale including those in various industrialfurnaces and incinerators but also unused waste heat on a small scalesuch as exhaust gas from various cogenerations, water heaters andautomobiles, and natural energy (e.g., ground heat, solar heat), andthis is a very effective measure against global warming.

According to the fourth aspect in the present invention, ahigh-efficiency thermoelectric conversion material can be produced at alow cost, and a thermoelectric conversion element of practical level canbe provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a strip casting apparatus used forthe production of alloy by quench-solidification.

FIG. 2 is a backscattered electron image of quench-solidified TiNiSnalloy.

FIG. 3 is an X-ray diffraction pattern of quench-solidified TiNiSnalloy.

FIG. 4 is a backscattered electron image of normally cooled TiNiSnalloy.

FIG. 5 is a backscattered electron image of quench-solidified Fe₂VAlalloy.

FIG. 6 is an X-ray diffraction pattern of quench-solidified Fe₂VAlalloy.

FIG. 7 is a plan view showing one example of the thermoelectricconversion module.

FIG. 8 is a view showing one example of the process for producingthermoelectric element and module for the generation of heat.

FIG. 9 is an X-ray diffraction pattern of the LaFe₄Sb₁₂ filledskutterudite alloy obtained by the present invention.

FIG. 10 is a backscattered electron image of the cross section of theLaFe₄Sb₁₂ filled skutterudite alloy obtained by the present invention.

FIG. 11 is a graph showing the relationship between the power factor andthe temperature of the p-type La(Fe_(1-x)M_(x))₄Sb₁₂ filled skutteruditethermoelectric conversion element obtained by the present invention.

FIG. 12 is a graph showing the relationship between the power factor andthe temperature of the n-type Ce(Co_(1-x)M_(x))₄Sb₁₂ filled skutteruditethermoelectric conversion element obtained by the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the present invention will be explainedin detail below. It should be noted that the following mode may becombined with each other, if necessary.

The Heusler alloy according to the present invention is represented bythe formula: A_(3-X)B_(X)C, wherein A and B each is a transition metal,C is a Group III or IV element, and the space group is Fm3m. The halfHeusler alloy is represented by the formula: ABC, wherein A and B eachis similarly a transition metal, C is a Group III or IV metal, and thespace group is F43m.

The electrical properties and thermal properties of the Heusler alloyaccording to the present invention can be adjusted by adding, as anadditive, B, C, Mg, Cu, Zn or a rare earth metal such as Y, La, Ce, Nd,Pr, Dy, Tb, Ga and Yb. In a preferred embodiment in the presentinvention, the ratio of strongest peak of the Heusler phase or halfHeusler phase is preferably 85% or more, more preferably 90% or more.This peak ratio is defined by IHS/(IHS+IA+IB)×100(%) from a strongestpeak (IHS) of the measured Heusler phase or half Heusler phase, astrongest peak intensity (IA) of an impurity phase A and a strongestpeak intensity (IB) of an impurity phase B in the powder X-raydiffraction measurement.

When combining p-type and n-type thermoelectric semiconductorscomprising the Heusler alloy in the present invention, thesesemiconductors may be electrically connected through an electrode or maybe directly connected through an antidiffusion layer.

The crystal grain diameter of the thermoelectric semiconductor producedfrom the Heusler alloy is preferably smaller in view of reducing thethermal conductivity by the effect of lattice scattering, specifically,100 μm or less, and from the standpoint of preventing abnormal graingrowth due to excessive sintering, inhibiting dust explosion orenhancing powder-filling property, more preferably from 10 to 50 μm.

In grinding the Heusler alloy, the grinding method is not limited andknown methods all can be employed but, for example, a ball mill, a potmill, an attritor, a pin mill or a jet mill can be used.

The jet mill is preferred despite its relatively high grinding cost,because a continuous operation can be performed, a necessary measure forthe prevention of oxidation or dust explosion can be easily taken, andeven a fine powder of about 20 μm can be processed in a relatively shorttime.

The quench-solidified alloy obtained in the present invention has goodgrindability and therefore, a fine powder of 20 μm or less can beobtained in a shorter time at a high yield.

The shaping method of the alloy is not particularly limited, but when apowder of several μm obtained by pulverizing the alloy is shaped under apressure of 0.5 to 5.0 t/cm² and the obtained green compact is sinteredin an inert atmosphere at 1,100 to 1,400° C., a thermoelectricsemiconductor element comprising fine crystal grains having a crystalgrain diameter of 100 μm or less can be produced.

The powder produced from the alloy obtained as above already comprisesonly a Heusler or half Heusler phase and therefore, when shaped into agreen compact by uniaxial shaping and sintered in an inert gas such asargon or in vacuum, a sintered body comprising a Heusler structure or ahalf Heusler phase can be easily produced. By processing such a sinteredbody into a predetermined shape and connecting p-type and n-type, athermoelectric conversion module can be produced.

The thermoelectric conversion module 1A and thermoelectric powergenerating system, which are preferred embodiments in the presentinvention, are not particularly limited in their construction, butexamples thereof include a thermoelectric conversion system 1B shown inFIG. 7. As shown in FIG. 7, a heat exchanger 113A or 113B such as heatsink is provided on both sides of a thermoelectric conversion module 1Ato construct the system.

In the heat exchangers 113A and 113B, a plurality of fin materials areerected on one surface side of a substrate. In the case where thesubstrate is a metal plate, an insulating material 112 (insulatinglayer) is preferably disposed on the outer side surface of eachelectrode 110 or on the entire surface of the substrate so as to preventa plurality of electrodes 110 of the thermoelectric conversion module 1Afrom shorting. When a DC current is passed to the thermoelectricconversion module group 1B in this mode, the temperature becomes low atone part and becomes high at another part and therefore, this can beused as a cooling/heating source or a thermoelectric power generatingsystem.

The p-type semiconductor thermoelectric element 19A and n-typesemiconductor thermoelectric element 19B constituting the thermoelectricdevice are electrically connected, for example, in series or in parallelto fabricate a thermoelectric conversion module 1A. The high-temperaturecontact side of the fabricated thermoelectric device is closelycontacted with the heat exchanger 113A on the waste heat side through aninsulator, and the low-temperature contact side of the thermoelectricdevice is closely contacted with the heat exchanger 113B on the coolingwater side through an insulator.

In the thus-fabricated thermoelectric conversion system 1B, atemperature difference is generated in each of the p-type semiconductorthermoelectric element 19A and n-type semiconductor thermoelectricelement 19B connected to the high-temperature contact side andlow-temperature contact side, as a result, electricity according to thetemperature difference based on the Seebeck effect is generated bythermoelectric conversion.

When the thermoelectric conversion system 1B produced by the presentinvention is employed, not only waste heat on a large scale includingthose in various industrial furnaces and incinerators but also wasteheat such as exhaust gas from various cogenerations, water heaters andautomobiles, and natural energy (e.g., ground heat, solar heat) can beutilized with high efficiency. Accordingly, the thermoelectricconversion module 1A in the present invention is suitable for waste heatrecovery system, solar heat utilizing system and Peltier cooling/heatingsystem.

The rare earth alloy in the present invention isRE_(x)(Fe_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member ofLa and Ce, M is at least one member selected from the group consistingof Ti, Zr, Sn and Pb, 0<x≦1, and 0<y<1). This alloy is suitably used asa p-type thermoelectric conversion material. The rare earth alloy in thepresent invention may contain therein unavoidable impurities such as Pb,As, Si, Al, Fe, Mo, W, C, O and N, and may take any shape of thin film,alloy and sintered body. The crystal structure is preferably askutterudite-type crystal structure. In the rare earth alloy in thepresent invention, if x is less than 0.01, the thermal conductivity isdeteriorated and the properties are impaired, and if y exceeds 0.15,this causes serious reduction in both the Seebeck coefficient and theelectric conductivity. Therefore, y is preferably 0.15 or less. Also, ify is less than 0.01, the enhancement of performance obtainable by theaddition is insufficient. Therefore, y is preferably 0.01 or more. WhenM is added within this range, the Seebeck coefficient and the electricconductivity both can be enhanced.

In another embodiment, the rare earth alloy in the present invention isRE_(x)(Co_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member ofLa and Ce, M is at least one member selected from the group consistingof Ti, Zr, Sn and Pb, 0<x≦1 and 0<y<1). This alloy is suitably used asan n-type thermoelectric conversion material. This rare earth alloy maycontain therein unavoidable impurities such as Pb, As, Si, Al, Fe, Mo,W, C, O and N, and may be in any shape of thin film, alloy and sinteredbody. The crystal structure is preferably a skutterudite-type crystalstructure. In this rare earth alloy, if x is less than 0.01, the thermalconductivity is deteriorated and the properties are impaired, and if yexceeds 0.15, this causes serious reduction in both the Seebeckcoefficient and the electric conductivity. Therefore, y is preferably0.15 or less. Also, if y is less than 0.01, the enhancement ofperformance obtainable by the addition is insufficient. Therefore, y ispreferably 0.01 or more. When M is added within this range, mainly theSeebeck coefficient and in turn the performance can be enhanced.

The rare earth alloy in the present invention can be produced byweighing raw materials to give a composition ofRE_(x)(Fe_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member ofLa and Ce, M is at least one member selected from the group consistingof Ti, Zr, Sn and Pb, 0<x≦1, and 0<y<1), melting the raw materials in aninert gas atmosphere, and then quench-solidifying the melt.

The rare earth alloy in the present invention can also be produced byweighing raw materials to give a composition ofRE_(x)(Co_(1-y)M_(y))₄Sb₁₂ (wherein RE is at least either one member ofLa and Ce, M is at least one member selected from the group consistingof Ti, Zr, Sn and Pb, 0<x≦1, and 0<y<1), melting the raw materials in aninert gas atmosphere, and then quench-solidifying the melt.

For the quenching in these two processes, a strip casting method shownin FIG. 1 or a method known as a quenching method for molten metals canbe used. The cooling rate is, in the range from 1,400 to 800° C.,preferably 1×10²° C./sec or more, more preferably from 1×10² to 1×10⁴°C./sec, still more preferably from 2×10² to 1×10³° C./sec. If thecooling rate is less than 1×10²° C./sec, the phases are separated andthe components greatly fluctuate by the grinding, whereas if it exceeds1×10⁴° C., the phase becomes amorphous and the grinding ratedisadvantageously decreases.

When the above-described quenching method is employed, the averagethickness of the alloy flake becomes approximately from 0.1 to 2 mm,preferably on the order of 0.2 to 0.4 mm. By employing a most preferredquenching rate, an average thickness on the order of 0.25 to 0.35 mm isobtained.

When the p-type and n-type thermoelectric conversion materials using therare earth alloys in the present invention are combined and contacted,for example, in a horseshoe shape to form a p-n junction element, ahigh-efficiency thermoelectric conversion element can be produced. Also,a thermoelectric conversion element advantageous in view of cost andresources as compared with conventional thermoelectric conversionelements can be produced.

FIG. 8 shows the process of producing the thermoelectric conversionelement and module in the present invention.

The thermoelectric conversion module and thermoelectric conversionsystem produced from the thermoelectric conversion element which is apreferred embodiment in the present invention are not particularlylimited in their construction but, for example, a system shown in FIG. 7may be fabricated. The p-type thermoelectric conversion element andn-type thermoelectric conversion element constituting the thermoelectricconversion device are electrically connected, for example, in series orin parallel to fabricate a thermoelectric conversion module. Thehigh-temperature contact side of the fabricated thermoelectricconversion device is closely contacted with the heat exchanger on thewaste heat side through an insulator, and the low-temperature contactside of the thermoelectric conversion device is closely contacted withthe heat exchanger on the cooling water side through an insulator.

In the thus-fabricated thermoelectric conversion system, a temperaturedifference is generated in each of the p-type thermoelectric conversionelement and n-type thermoelectric conversion element connected to thehigh-temperature contact side and low-temperature contact side, as aresult, electricity according to the temperature difference based on theSeebeck effect is generated by thermoelectric conversion.

When the thermoelectric conversion system produced by the presentinvention is employed, not only waste heat on a large scale includingthose in various industrial furnaces and incinerators but also wasteheat such as exhaust gas from various cogenerations, water heaters andautomobiles, and natural energy (e.g., ground heat, solar heat) can beutilized with high efficiency.

The filled skutterudite-based alloy for use in the present invention isan alloy represented by the formula: RT₄Sb₁₂ (wherein R is at least onemember selected from La, Ce, Pr, Nd, Sm, Eu and Yb, and T is at leastone member selected from Fe, Co, Ni, Os, Ru, Pd, Pt and Ag), where afilled skutterudite phase occupies 95% or more by volume. A part of Sbmay be replaced by As or P.

With respect to the raw materials which can be used for the filledskutterudite-based alloy in the present invention, the rare earth metalR may be a rare earth metal (purity: 90 mass % or more, balance ofunavoidable impurities such as Al, Fe, Mo, W, C, O and N), a mischmetal(rare earth metal component: 90 mass % or more, balance of unavoidableimpurities such as Al, Fe, Mo, W, C, O and N) or the like. Thetransition metal T may be a pure iron (purity: 99 mass % or more), ametal such as Co and Ni (purity: 99 mass % or more), or the like. The Sbmay be a metal antimony (purity: 95 mass % or more, balance ofunavoidable impurities such as Pb, As, Fe, Cu, Bi, Ni, C, O and N). Theraw materials for the filled skutterudite-based alloy in the presentinvention are prepared by weighing the above-described raw materials ofR, T and metal antimony to give an alloy composition of RT₄Sb₁₂. Forproducing the alloy in the present invention, the compositional ratio ofraw materials is preferably such that R is from 7.5 to 8.3 mass %, T isfrom 12.1 to 12.3 mass %, and Sb is from 79.5 to 80.2 mass %.

In the present invention, the filled skutterudite-based alloy isproduced by the strip casting method (SC method). FIG. 1 shows aproduction apparatus employing the SC method, which is used for theproduction of the alloy. In FIG. 1, 11 is a crucible, 12 is a tundish,13 is a copper roll, 14 is a container, 16 is a molten metal, and 15 isa solidified alloy flake.

In the production method of the filled skutterudite-based alloy for usein the present invention, the alloy raw materials prepared as above aremelted in the crucible 11 at a temperature of 800 to 1,800° C. in aninert gas atmosphere such as Ar and He. At this time, the pressure inthe atmosphere is preferably set to from atmospheric pressure (0.1 MPa)to 0.2 MPa, because the amount of Sb evaporated can be suppressed.

The molten metal 16 resulting from melting the alloy raw materials ispassed through the tundish 12 and poured on the water-cooled copper roll13 rotating in the arrow direction of FIG. 1, thereby effectingquench-solidification. At this time, the cooling rate is, in the rangefrom the temperature of the molten metal to 800° C., preferably from 10²to 10⁴° C./sec so as to obtain a uniform alloy structure comprising afilled skutterudite phase. The cooling rate is more preferably from5×10² to 3×10³° C./sec. The cooling rate of the molten alloy can becontrolled to a desired value by controlling the peripheral velocity ofthe copper roll 13 or the amount of the molten metal poured on thecopper roll 13.

The alloy resulting from solidification of the molten metal is separatedfrom the copper roll 13, and the obtained alloy flake 15 is accumulatedin the recovery box 14, cooled to room temperature in the recovery box14 and then taken out. At this time, when the recovery box 14 isthermally insulated or enforcedly cooled, the cooling rate of the alloyflake after solidification can be controlled. By controlling the coolingrate of the alloy flake after solidification in this way, the uniformityof the filled skutterudite phase in the alloy can be more enhanced.

In the present invention, the thickness of the filled skutterudite-basedalloy flake produced by the SC method is preferably set to 0.1 to 2 mm.By setting the thickness of the alloy flake to 0.1 to 2 mm, a filledskutterudite-based alloy having a sufficiently high mechanical strengthand facilitating the processing in use for a thermoelectric conversionelement can be obtained.

In the thus-produced skutterudite-based alloy for use in the presentinvention, when the produced phases are identified by the powder X-raydiffraction method, the intensity ratio of the strongest peak of thefilled skutterudite phase is 95% or more in the as-taken out state fromthe production apparatus of SC method even without newly applying a heattreatment. One example of the produced phases of the filledskutterudite-based alloy for use in the present invention as identifiedby the powder X-ray diffraction method is shown in FIG. 9.

FIG. 9 is a view showing the results of X-ray diffraction measurementwhen the alloy in the as-taken out state from the production apparatusof SC method is ground and measured. The integrated intensity of peaksshowing the highest intensity of the filled skutterudite phase and theintegrated intensities of peaks showing the highest intensities of otherphases such as Sb₂Fe and Sb are calculated, and the ratio of the filledskutterudite phase to the total of other phases is calculated, wherebythe abundance ratio of the filled skutterudite phase can be determined.For example, in the X-ray diffraction pattern shown in FIG. 9, theabundance ratio of the filled skutterudite phase is 99 mass % or more.

In the filled skutterudite-based alloy produced as above for use in thepresent invention, the filled skutterudite phase occupies 95% or more byvolume, and the ratio of phases other than the filled skutterudite phaseis 5% or less by volume. Here, the phase other than the filledskutterudite phase is, for example, phases of Sb₂Fe and Sb. Also, in thealloy for use in the present invention, the maximum diameter of phasesother than the filled skutterudite phase is 10 μm or less.

The volume ratio of the filled skutterudite phase to phases other thanthe filled skutterudite phase in the alloy can be determined bycalculating the area ratio of the region having a contrast differingfrom the filled skutterudite phase in a backscattered electron imagethrough a scanning electron microscope, and calculating the volume ratiofrom the obtained value. By using the backscattered electron image, themaximum diameter of phases other than the filled skutterudite phase canalso be determined. FIG. 10 shows one example of the backscatteredelectron image by a scanning electron microscope of the filledskutterudite-base alloy for use in the present invention. It is seenthat the alloy comprises a nearly uniform filled skutterudite phase, thevolume ratio is 95 vol % or more, and the maximum diameter of phasesother than the filled skutterudite phase is 10 μm or less.

The filled skutterudite-based alloy in the present invention is producedthrough melting and casting in an inert gas atmosphere and therefore,the total of oxygen, nitrogen and carbon contents can be made to 0.2mass % or less.

In the case of producing a thermoelectric conversion element, the filledskutterudite-based alloy obtained in the present invention can besuitably used as a p-type material. As for the n-type material, anexisting substance other than the filled skutterudite-based alloy, suchas Pb—Te-based material, can be used. When these p-type and n-typethermoelectric conversion materials are joined directly or indirectlythrough a metal conductor to create p-n junction, a thermoelectricconversion element can be produced. In the case of producing athermoelectric element module, these materials can be used incombination with a Bi—Te-based material or Se-based compound havingexcellent low-temperature properties and a Co oxide-based compoundhaving excellent high-temperature properties.

The production method of the thermoelectric conversion element is notparticularly limited but, for example, the production process shown inFIG. 8 can be employed.

The thermoelectric conversion module and thermoelectric conversionsystem produced from the thermoelectric conversion element which is apreferred embodiment in the present invention are not particularlylimited in their construction but, for example, a system shown in FIG. 7may be fabricated. The p-type semiconductor and n-type semiconductorconstituting the thermoelectric conversion device are electricallyconnected, for example, in series or in parallel to fabricate athermoelectric conversion module. The high-temperature contact side ofthe fabricated thermoelectric conversion device is closely contactedwith the heat exchanger on the waste heat side through an insulator, andthe low-temperature contact side of the thermoelectric conversion deviceis closely contacted with the heat exchanger on the cooling water sidethrough an insulator.

In the thus-fabricated thermoelectric conversion system, a temperaturedifference is generated in each of the p-type semiconductor and n-typesemiconductor connected to the high-temperature contact side andlow-temperature contact side, as a result, electricity according to thetemperature difference based on the Seebeck effect is generated bythermoelectric conversion.

When the thermoelectric conversion system produced by the presentinvention is employed, not only waste heat on a large scale includingthose in various industrial furnaces and incinerators but also wasteheat such as exhaust gas from various cogenerations, water heaters andautomobiles, and natural energy (e.g., ground heat, solar heat) can beutilized with high efficiency.

The rare earth-containing alloy in the present invention isLa(Fe_(1-x)M_(x))₄Sb₁₂, wherein M is at least one member selected fromTi, Zr, Sn and Pb, and x is 0<x<1, preferably 0.01≦x≦0.15. This alloy issuitably used as a p-type thermoelectric conversion material. The rareearth-containing alloy in the present invention may contain thereinunavoidable impurities such as Pb, As, Si, Al, Fe, Mo, W, C, O and N,and may take any shape of thin film, alloy and sintered body. Thecrystal structure may be a skutterudite-type crystal structure but ispreferably a filled skutterudite-type crystal structure. In the rareearth-containing alloy in the present invention, if x exceeds 0.15, thiscauses serious reduction in both the Seebeck coefficient and theelectric conductivity. Therefore, x is preferably 0.15 or less. When Mis added within this range, the Seebeck coefficient and the electricconductivity both can be enhanced.

In another embodiment, the rare earth-containing alloy in the presentinvention is Ce(Co_(1-x)M_(x))₄Sb₁₂, wherein M is at least one memberselected from Cu, Zn and Mn, and x is 0<x<1, preferably from 0.01 to0.15. This alloy is suitably used as an n-type thermoelectric conversionmaterial. This rare earth-containing alloy may contain thereinunavoidable impurities such as Pb, As, Si, Al, Fe, Mo, W, C, O and N,and may take any shape of thin film, alloy and sintered body. Thecrystal structure may be a skutterudite-type crystal structure but ispreferably a filled skutterudite-type crystal structure. In this rareearth-containing alloy, if x exceeds 0.15, this causes serious reductionin both the Seebeck coefficient and the electric conductivity.Therefore, x is preferably 0.15 or less. When M is added within thisrange, mainly the Seebeck coefficient and in turn the performance can beenhanced.

The rare earth-containing alloy in the present invention can be producedby weighing raw materials to give a composition ofLa(Fe_(1-x)M_(x))₄Sb₁₂ (wherein M is at least one member selected fromthe group consisting of Ti, Zr, Sn and Pb), melting the raw materials inan inert gas atmosphere, and then quench-solidifying the melt.

The rare earth alloy in the present invention can also be produced byweighing raw materials to give a composition of Ce(Co_(1-x)M_(x))₄Sb₁₂(wherein M is at least one member selected from the group consisting ofCu, Zn and Mn), melting the raw materials in an inert gas atmosphere,and then quench-solidifying the melt.

For the quenching in these two methods, a strip casting method shown inFIG. 1 or a method known as a quenching method for molten metals can beused. The cooling rate from 1,500 to 700° C. is preferably 10² to 10³°C./sec.

When the p-type and n-type thermoelectric conversion materials using therare earth-containing alloys in the present invention are combined andcontacted, for example, in a horseshoe shape to form a p-n junctionelement, a high-efficiency thermoelectric conversion element can beproduced. Also, a thermoelectric conversion element advantageous in viewof cost and resources as compared with conventional thermoelectricconversion elements can be produced.

The present invention is described in greater detail below by referringto Examples, but the present invention is not limited to these Examples.

Example 1

Sponge Ti (purity: 99 mass % or more), sponge Zr (purity: 99 mass % ormore), electrolytic Ni (purity: 99 mass % or more) and Sn metal (purity:99.9 mass % or more) were weighed to give a half Heusler-type(Ti_(x)Zr_(1-x))NiSn composition after casting, and high-frequencymelted at a temperature up to 1,700° C. under 0.1 MPa in an Aratmosphere. Thereafter, by using a strip casting apparatus 120 shown inFIG. 1, the molten metal was poured from the crucible 11 through thetundish 12 on the water-cooled copper roll 13 rotating at a sphericalvelocity of 0.9 m/sec to produce an alloy flake 15, and the alloy flakewas recovered in the recovery box 14. The average thickness of the alloyflake 15 was 0.25 mm. In this casting, the cooling rate was estimated tobe about 7×10²° C./sec.

FIG. 2 is a reflection electron microphotograph showing the crosssection of the alloy obtained as above. As seen from this, the alloyflake has a uniform structure in the entire region. Also, it is knownfrom the X-ray diffraction pattern of FIG. 3 that the structure is ahalf Heusler structure. The ratio of strongest peak of the TiNiSn halfHeusler phase was 100%.

This alloy was ground to 200 μm or less by a disc mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100NP™manufactured by Nippon Pneumatic Mfg. Co., Ltd. The average particlesize d50 of the obtained powder was 3.0 μm. The yield of the powder was80% based on the amount charged.

The obtained powder was shaped into a size of 15 mm×15 mm×30 mm under ashaping pressure of 1.0 t/cm² by a shaping machine in a glove boxcontrolled to an oxygen concentration of 300 ppm or less, and then keptat 1,200° C. for 3 hours in vacuum, thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient α, electric conductivity ρ andpower factor Pf=α²/ρ at 200 to 500° C. by using a thermoelectricproperty evaluating apparatus, ZEM-2™ manufactured by ULVAC, Inc. Thesemeasurement results are shown in Table 1.

TABLE 1 Thermoelectric Properties of Heusler Element Fe—V—Al Tem- Resis-Seebeck pera- tivity Coefficient Power ture of (σ = (α = Factor TypeSample Sample Ω · m) V/° C.) (α²σ⁻¹) n Fe₂V(Al_(0.8)Si_(0.2)) 53.62.40E−06 −9.71E−05 3.94E−03 101.0 2.68E−06 −9.84E−05 3.61E−03 198.93.16E−06 −9.63E−05 2.93E−03 297.2 3.40E−06 −7.87E−05 1.82E−03 395.33.43E−06 −5.99E−05 1.05E−03 Fe₂V(Al_(0.8)Si_(0.2)) 54.6 2.36E−06−9.99E−05 4.23E−03 100.9 2.62E−06 −1.02E−04 4.00E−03 198.6 3.08E−06−9.79E−05 3.11E−03 296.8 3.32E−06 −7.94E−05 1.90E−03 395.0 3.34E−06−6.07E−05 1.10E−03 Fe₂V(Al_(0.9)Si_(0.1)) 54.2 3.89E−06 −1.18E−043.58E−03 101.7 4.20E−06 −1.11E−04 2.95E−03 200.0 4.47E−06 −8.92E−051.78E−03 298.8 4.33E−06 −8.15E−05 8.72E−04 397.1 4.09E−06 −4.19E−054.30E−04 Fe₂V(Al_(0.9)Si_(0.1)) 55.2 3.77E−06 −1.18E−04 3.71E−03 101.04.03E−06 −1.12E−04 3.10E−03 198.6 4.28E−06 −9.10E−05 1.93E−03 296.94.16E−06 −6.27E−05 9.45E−04 395.0 3.92E−06 −4.32E−05 4.76E−04 Fe₂VA154.3 9.02E−06 −6.02E−05 4.02E−04 100.8 7.72E−06 −4.34E−05 2.44E−04 197.55.81E−06 −2.44E−05 1.03E−04 295.0 4.72E−06 −1.57E−05 5.24E−05 392.54.11E−06 −1.31E−05 4.16E−05 489.9 3.75E−06 −1.25E−05 4.18E−05 Fe₂VA154.6 9.21E−06 −5.97E−05 3.87E−04 101.2 7.82E−06 −4.31E−05 2.38E−04 198.25.80E−06 −2.40E−05 9.95E−05 295.8 4.68E−06 −1.57E−05 5.26E−05 393.24.07E−06 −1.30E−05 4.15E−05 490.7 3.71E−06 −1.29E−05 4.46E−05 pFe₂(V_(0.9)Ti_(0.1))Al 55.1 2.33E−06 7.01E−05 2.11E−03 101.9 2.55E−067.29E−05 2.09E−03 199.9 2.94E−06 7.27E−05 1.80E−03 298.4 3.11E−065.58E−05 1.00E−03 396.6 3.12E−06 3.53E−05 3.99E−04Fe₂(V_(0.97)Ti_(0.03))Al 54.8 7.43E−06 6.74E−05 6.11E−04 101.5 6.69E−065.74E−05 4.92E−04 199.4 5.40E−06 3.63E−05 2.43E−04 297.9 4.57E−061.88E−05 7.73E−05 396.0 4.12E−06 7.53E−06 1.38E−05 494.0 3.84E−063.83E−07 3.81E−08 Fe₂(V_(0.97)Ti_(0.03))Al 54.9 9.28E−06 7.89E−056.70E−04 101.2 8.51E−06 6.90E−05 5.59E−04 198.8 6.95E−06 4.47E−052.87E−04 297.1 5.88E−06 2.42E−05 9.99E−05 395.2 5.29E−06 1.08E−052.21E−05

Comparative Example 1

Sponge Ti (purity: 99 mass % or more), sponge Zr (purity: 99 mass % ormore), electrolytic Ni (purity: 99 mass % or more) and Sn metal (purity:99.9 mass % or more) were weighed to give a half Heusler-type(Ti_(x)Zr_(1-x))NiSn composition after casting, and high-frequencymelted at a temperature up to 1,700° C. under 0.1 MPa in an Aratmosphere. Thereafter, the alloy was solidified by using a cast ironmold in a width of 20 mm. The cooling rate at this time was estimated tobe about 1×10²° C./sec.

FIG. 4 is a reflection electron microphotograph showing the crosssection of the alloy obtained as above. As seen from this, a pluralityof phases non-uniformly are present in the alloy. The ratio of strongestpeak of the half Heusler phase was 80%.

A block of 4 mm×4 mm×15 mm was cut out from the alloy flake aftercasting and measured for the Seebeck coefficient α, electricconductivity ρ and power factor Pf=α²/ρ at 200 to 500° C. by using athermoelectric property evaluating apparatus, ZEM-2™ manufactured byULVAC, Inc. These measurement results are shown in Table 2. As seen fromthese results, the performance was apparently decreased as compared withExample 1.

TABLE 2 Thermoelectric Properties of Half Heusler Element Ti—Ni—Sn Tem-Resis- Seebeck pera- tivity Coefficient Power ture of (σ = (α = FactorType Sample Sample Ω · m) V/° C.) (α²σ⁻¹) N (Ti_(0.5)Zr_(0.5)) 198.11.41E−05 −2.10E−04 3.14E−03 NiSn_(0.998)Sb_(0.002) 296.4 1.42E−05−2.16E−04 3.29E−03 394.5 1.37E−05 −2.17E−04 3.43E−03 492.5 1.32E−05−2.12E−04 3.41E−03 (Ti_(0.5)Zr_(0.5)) 198.5 1.43E−05 −2.11E−04 3.11E−03NiSn_(0.998)Sb_(0.002) 296.8 1.44E−05 −2.17E−04 3.26E−03 394.9 1.39E−05−2.15E−04 3.35E−03 492.9 1.33E−05 −2.12E−04 3.36E−03 (Ti_(0.5)Zr_(0.5))198.0 1.37E−05 −2.07E−04 3.14E−03 NiSn_(0.998)Sb_(0.002) 296.4 1.37E−05−2.14E−04 3.32E−03 394.5 1.32E−05 −2.14E−04 3.47E−03 492.4 1.27E−05−2.11E−04 3.49E−03 (Ti_(0.5)Zr_(0.5))NiSn 198.3 1.67E−05 −1.92E−042.20E−03 296.5 1.62E−05 −2.01E−04 2.49E−03 394.5 1.49E−05 −2.04E−042.78E−03 492.4 1.39E−05 −1.98E−04 2.82E−03 (Ti_(0.5)Zr_(0.5))NiSn 197.81.70E−05 −1.92E−04 2.17E−03 296.0 1.64E−05 −2.02E−04 2.49E−03 394.21.51E−05 −2.04E−04 2.76E−03 492.0 1.41E−05 −1.99E−04 2.82E−03(Ti_(0.5)Zr_(0.5))NiSn 197.9 1.69E−05 −1.89E−04 2.12E−03 296.1 1.64E−05−2.01E−04 2.45E−03 394.2 1.51E−05 −2.03E−04 2.71E−03 492.1 1.41E−05−1.97E−04 2.76E−03 590.7 1.30E−05 −1.81E−04 2.53E−03 TiNiSn 199.24.45E−06 −7.33E−05 1.21E−03 297.7 4.64E−06 −7.94E−05 1.36E−03 395.94.64E−06 −8.36E−05 1.51E−03 493.9 4.71E−06 −8.40E−05 1.50E−03 TiNiSn198.6 4.50E−06 −7.17E−05 1.14E−03 297.0 4.68E−06 −7.77E−05 1.29E−03395.2 4.67E−06 −8.11E−05 1.41E−03 493.2 4.74E−06 −8.30E−05 1.45E−03TiNiSn 198.4 4.39E−06 −7.20E−05 1.18E−03 296.7 4.58E−06 −7.93E−051.37E−03 394.8 4.58E−06 −8.36E−06 1.53E−03 492.8 4.64E−06 −8.47E−051.55E−03 (Ti_(0.5)Zr_(0.5)) 198.5 5.04E−06 −4.87E−05 4.70E−04 NiSn Bookmold 296.9 5.46E−06 −6.69E−05 8.21E−04 alloy 395.1 5.30E−06 −7.92E−061.18E−03 493.0 5.23E−06 −8.07E−05 1.24E−03

Example 2

Electrolytic iron (purity: 99 mass % or more), ferrovanadium (Fe—V, HSFV1, V purity: 87 mass %) and Al metal were weighed to give aHeusler-type Fe₂(V_(x)Ti_(1-x))(Al_(y)Si_(1-y)) (0<x<1, 0<y<1)composition after casting, and high-frequency melted at a temperature upto 1,700° C. under 0.1 MPa in an Ar atmosphere. Thereafter, by using astrip casting apparatus 120 shown in FIG. 1, the molten metal was pouredfrom the crucible 11 through the tundish 12 on the water-cooled copperroll 13 rotating at a spherical velocity of 0.9 m/sec to produce analloy flake 15, and the alloy flake was recovered in the recovery box14. The average thickness of the alloy flake 15 was 0.28 mm. In thiscasting, the cooling rate was estimated to be about 7×10²° C./sec.

FIG. 5 is a backscattered electron image showing the cross section ofthe alloy obtained, and FIG. 6 is a powder X-ray diffraction pattern ofthe alloy. As seen from these, a Heusler alloy comprising a single phasecan be obtained by the quench-solidification method. The ratio ofstrongest peak of the Fe₂VAl was 100%.

This alloy was ground to 200 μm or less by a stamp mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100NP™manufactured by Nippon Pneumatic Mfg. Co., Ltd. The average particlesize d50 of the obtained powder was 13 μm. The yield of the powder was60% based on the amount charged. The obtained powder was shaped into asize of 15 mm×15 mm×30 mm under a shaping pressure of 3.0 t/cm² by ashaping machine in a glove box controlled to an oxygen concentration of300 ppm or less, and then kept at 1,380° C. for 3 hours in vacuum,thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient α, electric conductivity ρ andpower factor Pf=α²/ρ at 200 to 500° C. by using a thermoelectricproperty evaluating apparatus, ZEM-2™ manufactured by ULVAC, Inc. Thesemeasurement results are shown in Table 3.

Test Example 1

La metal (purity: 95 mass % or more, balance of Ce and unavoidableimpurities) was used as the rare earth metal, and electrolytic iron(purity: 99 mass % or more), Sb metal (purity: 99 mass % or more) andsubstituting metal M (purity: 99 mass % or more) were weighed to give areplacement ratio shown in Table 1. These metals were melted at atemperature up to 1,400° C. under 0.1 MPa in an Ar atmosphere.Thereafter, the molten metal was cast to produce an alloy flake by usinga strip casting apparatus shown in FIG. 1. At this time, the moltenmetal was poured on the water-cooled copper roll rotating at aperipheral velocity of 0.92 m/sec under the conditions such that thecrosswise width was 85 mm and the poured amount of molten metal was 150g/sec. The average thickness of the alloy flake was from 0.26 to 0.28mm. The cooling rate of the molten metal from 1,400° C. to 800° C. wasabout 600° C./sec, that is, the time required for cooling from 1,400° C.to 800° C. was about 1 second.

This alloy was ground to 200 μm or less by a disc mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100NP™manufactured by Nippon Pneumatic Mfg. Co., Ltd. At this time, d50 wasfrom 2.5 to 4.0 μm.

The obtained powder was shaped into a size of about 15 mm×15 mm×30 mm bya shaping machine in a glove box controlled to an oxygen concentrationof 300 ppm or less, and then kept at 780 to 820° C. for 3 hours in anargon stream, thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient and electric conductivity in therange of 200 to 500° C. by using a thermoelectric property evaluatingapparatus, ZEM-2™ manufactured by ULVAC, Inc., and the power factorPf=α²/ρ was calculated. Out of these measurement results, thethermoelectric properties at 489° C. are shown in Table 3.

In Table 3, based on the sample where x=1.0 and y=0, when the powerfactor surpassed the basis, this was judged “effective” (∘), and whenlower than the basis, this was judged “not effective” (×).

Test Example 2

Ce metal (purity: 95% or more, balance of La and unavoidable impurities)was used as the rare earth metal, and Co metal (purity: 99 mass % ormore), Sb metal (purity: 99 mass % or more) and substituting metal M(purity: 99 mass % or more) were weighed to give a replacement ratioshown in Table 4. These metals were melted at a temperature up to 1,400°C. under 0.1 MPa in an Ar atmosphere. Thereafter, the molten metal wascast to produce an alloy flake by using a strip casting apparatus shownin FIG. 1. At this time, the molten metal was poured on the water-cooledcopper roll rotating at a peripheral velocity of 0.92 m/sec under theconditions such that the crosswise width was 85 mm and the poured amountof molten metal was 150 g/sec. The average thickness of the alloy flakewas the same as in Test Example 1.

This alloy was ground to 200 μm or less by a disc mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100NP™manufactured by Nippon Pneumatic Mfg. Co., Ltd. At this time, d50 wasfrom 2.5 to 4.0 μm.

The obtained powder was shaped into a size of about 15 mm×15 mm×30 mm bya shaping machine in a glove box controlled to an oxygen concentrationof 300 ppm or less, and then kept at 870 to 920° C. for 3 hours in anargon stream, thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient and electric conductivity in therange of 200 to 500° C. by using a thermoelectric property evaluatingapparatus, ZEM-2™ manufactured by ULVAC, Inc., and the power factorPf=α²/ρ was calculated. Out of these measurement results, thethermoelectric properties at 489° C. are shown in Table 4.

In Table 1, based on the sample where x=1.0 and y=0, when the powerfactor surpassed the basis, this was judged “effective” (∘), and whenlower than the basis, this was judged “not effective” (×).

TABLE 3 RE_(x)(Fe_(1−y)M_(y))₄Sb₁₂ Rare Earth Seebeck Co- Power MetalSubstituting Resistivity efficient α Factor RE Ratio x Metal M Ratio y ρ(Ω · m) (V/° C.) Pf = α²/ρ Judgment La 1.00 none 6.32E−06 1.14E−042.07E−03 basis Sn 0.020 5.43E−06 1.11E−04 2.28E−03 ∘ 0.040 5.91E−061.20E−04 2.45E−03 ∘ Pb 0.002 6.90E−06 1.26E−04 2.29E−03 ∘ 0.011 6.96E−061.28E−04 2.34E−03 ∘ 0.023 6.21E−06 1.21E−04 2.35E−03 ∘ Ti 0.010 5.45E−061.15E−04 2.44E−03 ∘ 0.047 6.42E−06 1.26E−04 2.46E−03 ∘ 0.094 5.75E−061.24E−04 2.67E−03 ∘ 0.140 5.67E−06 1.13E−04 2.24E−03 ∘ Zr 0.025 6.19E−061.25E−04 2.52E−03 ∘ 0.052 6.28E−06 1.22E−04 2.37E−03 ∘ Al 0.155 5.18E−069.38E−05 1.70E−03 x Si 0.150 4.49E−06 8.62E−05 1.66E−03 x 0.50 none3.60E−06 5.35E−05 7.95E−04 x 0.75 none 4.58E−06 7.81E−05 1.33E−03 x Yb1.00 none 3.81E−06 6.48E−05 1.06E−03 x Sm 1.00 none 3.89E−06 4.38E−054.94E−04 x Gd 1.00 none 3.81E−06 2.77E−05 2.01E−04 x

TABLE 4 RE_(x)(Co_(1−y)M_(y))₄Sb₁₂ Rare Earth Seebeck Co- Power MetalSubstituting Resistivity efficient α Factor RE Ratio x Metal M Ratio y ρ(Ω · m) (V/° C.) Pf = α²/ρ Judgment Ce 1.00 none 4.84E−06 −1.10E−042.51E−03 basis Cu 0.007 4.64E−06 −1.14E−04 2.81E−03 ∘ 0.036 4.58E−06−1.17E−04 3.00E−03 ∘ 0.073 4.83E−06 −1.15E−04 2.74E−03 ∘ Ni 0.0785.80E−06 −1.26E−04 2.73E−03 ∘ Zn 0.007 4.81E−06 −1.14E−04 2.71E−03 ∘0.035 5.75E−06 −1.26E−04 2.75E−03 ∘ 0.071 5.38E−06 −1.23E−04 2.79E−03 ∘Bi 0.023 1.06E−05 −1.32E−04 1.65E−03 x Mn 0.083 5.54E−06 −8.40E−051.27E−03 x Cu & 0.018 5.08E−06 −1.20E−04 2.84E−03 ∘ Zn 0.017 0.25 none3.26E−05 −2.21E−04 1.50E−03 x 0.50 none 6.62E−06 −1.58E−04 3.75E−03 ∘0.75 none 5.27E−06 −1.34E−04 3.38E−03 ∘ Yb 1.00 none 5.13E−06 −9.45E−051.74E−03 x Sm 1.00 none 1.12E−05 −1.18E−04 1.24E−03 x Gd 1.00 none3.33E−04 −4.67E−05 6.54E−06 x

Reference Example 1

La metal was used as the rare earth metal, and this metal andadditionally electrolytic iron and Sb were weighed to give astoichiometric composition of LaFe₄Sb₁₂, melted at a temperature up to1,400° C. under 0.1 MPa in an Ar atmosphere. Thereafter, the moltenmetal was cast to produce an alloy flake having a thickness of 0.28 mmby using a strip casting apparatus shown in FIG. 1. At this time, themolten metal was poured on the water-cooled copper roll rotating at aperipheral velocity of 0.92 m/sec under the conditions such that thecrosswise width was 85 mm and the pour rate was 150 g/sec. In thiscasting, the cooling rate was estimated to be about 1×103° C./sec.

When the produced alloy flake was ground and measured by powder X-raydiffraction, as shown in FIG. 9, the peak of Sb₂Fe or Sb was scarcelyobserved. The abundance ratio of the filled skutterudite phase wascalculated from this Figure, as a result, 98% or more was being occupiedby the LaFe₄Sb₁₂ filled skutterudite phase, and the ratio of Sb₂Fe was2% or less.

When this alloy flake was further heat-treated at 550° for 1 hour in anAr flow under atmospheric pressure, the LaFe₄Sb₁₂ filled skutteruditephase came to occupy almost 100% in the powder X-ray diffractionmeasurement. The fine structure and produced phases in the alloy afterheat treatment were confirmed in a backscattered electron image, as aresult, phase separation was not observed at all and the alloy wasalmost entirely constituted by a uniform filled skutterudite phase.

Reference Example 2

Mischmetal comprising 53 mass % of Ce and 47 mass % of La was used asthe rare earth metal, and this metal and additionally electrolytic ironand Sb (99%) were weighed to give a stoichiometric composition of(Ce_(x),La_(1-x))Fe₄Sb₁₂, melted at a temperature up to 1,400° C. under0.1 MPa in an Ar atmosphere. Thereafter, the molten metal was cast toproduce an alloy flake having a thickness of 0.28 mm by using a stripcasting apparatus shown in FIG. 1. At this time, the molten metal waspoured on the water-cooled copper roll rotating at a peripheral velocityof 0.92 m/sec under the conditions such that the crosswise width was 85mm and the pour rate was 150 g/sec.

When the produced alloy was ground and measured by powder X-raydiffraction, 98% or more in terms of the intensity ratio of strongestpeak was being occupied by the (Ce_(x),La_(1-x))Fe₄Sb₁₂ filledskutterudite phase, and the ratio of Sb₂Fe was 2% or less.

When immediately after casting of this alloy, the cooling rate of thecontainer was controlled in an Ar atmosphere under atmospheric pressureto be 2° C./sec in the range from 700° C. to 500° C., the(Ce_(x),La_(1-x))Fe₄Sb₁₂ filled skutterudite phase came to occupy 99% ormore in the powder X-ray diffraction measurement. The fine structure andproduced phases in the alloy after heat treatment were confirmed in abackscattered electron image, as a result, phase separation was notobserved at all and the entire alloy was constituted by a nearly uniformfilled skutterudite phase.

Reference Example 3

La metal was used as the rare earth metal, and this metal andadditionally electrolytic iron and Sb were weighed to give astoichiometric composition of LaFe₄Sb₁₂, melted at a temperature up to1,400° C. under 0.2 MPa in an Ar atmosphere. Thereafter, the moltenmetal was cast to produce an alloy flake having a thickness of 0.28 mmby using a strip casting apparatus shown in FIG. 1. At this time, themolten metal was poured on the water-cooled copper roll rotating at aperipheral velocity of 0.92 m/sec under the conditions such that thecrosswise width was 85 mm and the pour rate was 150 g/sec.

When the produced alloy flake was ground and measured by powder X-raydiffraction, 95% or more in terms of the intensity ratio of strongestpeak was being occupied by the LaFe₄Sb₁₂ filled skutterudite phase, andthe ratio of Sb₂Fe was 5% or less.

When this alloy flake was further heat-treated at 550° for 1 hour in anAr flow under atmospheric pressure, the LaFe₄Sb₁₂ filled skutteruditephase came to occupy 99% or more in the powder X-ray diffractionmeasurement. The fine structure and produced phases in the alloy afterheat treatment were confirmed in a backscattered electron image, as aresult, phase separation was not observed at all and the entire alloywas constituted by a nearly uniform filled skutterudite phase.

Example 3

The alloy described in Reference Example 3 was used as the p-typeelement, and CeCo₄Sb₁₂ was produced in the same manner as in ReferenceExamples 1 to 3 and used as the n-type element. Each alloy was ground bya jet mill to produce a powder having an average particle size of 2.5μm, shaped under a pressure of 1.2 t/cm², sintered at 800 to 900° C. inan argon flow and cut into a 2 mm-square element. After plating of Cu aselectrode and plating of Ti and Ni as antidiffusion layer, the elementswere joined together with an Ag solder at 700° C. to produce a module.

A module comprising 70 pairs of p and n elements was produced by usingthe device obtained above and measured, as a result, the conversionefficiency was 13% based on the heat input when the low-temperature sidewas 30° C. and the high-temperature side was 500° C.

Comparative Example 2

La metal was used as the rare earth metal, and this metal andadditionally electrolytic iron and Sb were weighed to give astoichiometric composition of LaFe₄Sb₁₂, melted at a temperature up to1,400° C. in a reduced pressure atmosphere. While keeping the reducedpressure, the molten metal was cast in the same manner as in Example 3to produce a strip cast alloy having a thickness of 0.28 mm, that is,the molten metal was poured on the water-cooled copper roll rotating ata peripheral velocity of 0.92 m/sec under the conditions such that thecrosswise width was 85 mm and the pour rate was 150 g/sec.

When the produced alloy was ground and measured by powder X-raydiffraction, almost the entire was being occupied by Sb₂Fe and Sb. Thisalloy was further heat-treated, and the fine structure and producedphases were confirmed in a backscattered electron image, as a result,the alloy was found to be constituted by a plurality of phases. Also,the oxygen concentration of this alloy exceeded 0.2 mass %, and theamount of Sb was short of the stoichiometric ratio. From these, it waspresumed that a filled skutterudite phase was not obtained because therare earth metal was eliminated from the skutterudite phase and Sb wasevaporated during melting to deviate from the stoichiometric ratio.

Comparative Example 3

La metal was used as the rare earth metal, and this metal andadditionally electrolytic iron and Sb were weighed to give astoichiometric composition of LaFe₄Sb₁₂, melted at a temperature up to1,400° C. under 0.1 MPa in an Ar atmosphere. Thereafter, the moltenmetal was poured on a book mold comprising a copper plate having a widthof 10 mm and a thickness of 20 mm, at a pour rate of 150 g/sec toproduce an alloy.

When the produced alloy was ground and measured by powder X-raydiffraction, almost the entire was being occupied by Sb₂Fe and Sb. Thisalloy was further heat-treated at 550° C. for 1 hour in an Ar flow underatmospheric pressure, but in the measurement by powder X-raydiffraction, the alloy was being still occupied mostly by Sb₂Fe and afilled skutterudite phase was scarcely observed. When the fine structureand produced phases were confirmed in a backscattered electron image,the alloy was found to be constituted by a plurality of phases. Theoxygen concentration of this alloy was 0.1 mass % or less and the amountof Sb was nearly stoichiometric, but it seemed that heat treatment for avery long time was necessary for causing this alloy to be constituted bya uniform filled skutterudite phase.

Comparative Example 4

Alloys for p-type LaFe₄Sb₁₂ and n-type CeCo₄Sb₁₂ elements were producedby the method of Comparative Example 3 and each alloy was ground by ajet mill without passing through heat treatment to obtain a powderhaving an average particle size of 2.5 μm, shaped under a pressure of1.2 t/cm², sintered at 800 to 900° C. in an argon flow and cut into a 2mm-square element. After plating of Cu as electrode and plating of Tiand Ni as antidiffusion layer, the elements were joined together with anAg solder at 700° C. to produce a module.

A module comprising 70 pairs of p and n elements was produced by usingthe device obtained above and measured, as a result, the conversionefficiency was 8% based on the heat input when the low-temperature sidewas 30° C. and the high-temperature side was 500° C.

Test Example 3

La metal (purity: 95 mass % or more) was used as the rare earth metal,and electrolytic iron (purity: 99 mass % or more), Sb metal (purity: 99mass % or more) and substituting metal M (purity: 99 mass % or more)were weighed to give a replacement ratio x shown in Table 5. Thesemetals were melted at a temperature up to 1,400° C. under 0.1 MPa in anAr atmosphere. Thereafter, the molten metal was cast to produce an alloyflake by using a strip casting apparatus shown in FIG. 1. At this time,the molten metal was poured on the water-cooled copper roll rotating ata peripheral velocity of 0.92 m/sec under the conditions such that thecrosswise width was 85 mm and the poured amount of molten metal was 150g/sec. The average thickness of the alloy flake was from 0.26 to 0.28mm.

This alloy was ground to 200 μm or less by a disc mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100™manufactured by Nippon Pneumatic Mfg. Co., Ltd. At this time, d50 wasfrom 2.5 to 4.0 μm.

The obtained powder was shaped into a size of about 15 mm×15 mm×30 mm bya shaping machine in a glove box controlled to an oxygen concentrationof 300 ppm or less, and then kept at 780 to 820° C. for 3 hours in anargon stream, thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient and electric conductivity in therange of 200 to 500° C. by using a thermoelectric property evaluatingapparatus, ZEM-2™ manufactured by ULVAC, Inc., and the power factorPf=α²/ρ was calculated. Out of these measurement results, thethermoelectric properties at 489° C. are shown in Table 5.

In Table 5, based on the sample where the metal was not replaced, whenthe power factor surpassed the basis, this was judged “effective” (⊚),and when lower than the basis, this was judged “not effective” (×).

Test Example 4

Ce metal (purity: 95% or more) was used as the rare earth metal, and Cometal (purity: 99% or more), Sb (purity: 99% or more) and substitutingmetal M (purity: 99% or more) were weighed to give a replacement ratio xshown in Table 6. These metals were melted at a temperature up to 1,400°C. under 0.1 MPa in an Ar atmosphere. Thereafter, the molten metal wascast to produce an alloy flake by using a strip casting apparatus shownin FIG. 1. At this time, the molten metal was poured on the water-cooledcopper roll rotating at a peripheral velocity of 0.92 m/sec under theconditions such that the crosswise width was 85 mm and the poured amountof molten metal was 150 g/sec. The average thickness of the alloy flakewas the same as in Test Example 3.

This alloy was ground to 200 μm or less by a disc mill and thenpulverized at 0.5 MPa in a nitrogen steam by a jet mill, NPK-100™manufactured by Nippon Pneumatic Mfg. Co., Ltd. At this time, d50 wasfrom 2.5 to 4.0 μm.

The obtained powder was shaped into a size of about 15 mm×15 mm×30 mm bya shaping machine in a glove box controlled to an oxygen concentrationof 300 ppm or less, and then kept at 870 to 920° C. for 3 hours in anargon stream, thereby obtaining a sintered body.

A block of 4 mm×4 mm×15 mm was cut out from the sintered body andmeasured for the Seebeck coefficient and electric conductivity in therange of 200 to 500° C. by using a thermoelectric property evaluatingapparatus, ZEM-2™ manufactured by ULVAC, Inc., and the power factorPf=α²/ρ was calculated. Out of these measurement results, thethermoelectric properties at 489° C. are shown in Table 6.

In Table 6, based on the sample where the metal was not replaced, whenthe power factor surpassed the basis, this was judged “effective” (⊚),and when lower than the basis, this was judged “not effective” (×).

TABLE 5 Seebeck Replace- Resis- Coeffi- Substituting ment tivity ρ cientα Power Judg- Metal M Ratio x (Ω · m) (V/° C.) Factor Pf ment Sn 0.0405.91E−06 1.20E−04 2.45E−03 ⊚ 0.020 5.43E−06 1.11E−04 2.28E−03 ⊚ Pb 0.0236.21E−06 1.21E−04 2.35E−03 ⊚ 0.011 6.96E−06 1.28E−04 2.34E−03 ⊚ 0.0026.90E−06 1.26E−04 2.29E−03 ⊚ Ti 0.140 5.67E−06 1.13E−04 2.24E−03 ⊚ 0.0945.75E−06 1.24E−04 2.67E−03 ⊚ 0.047 6.42E−06 1.26E−04 2.46E−03 ⊚ 0.0105.45E−06 1.15E−04 2.44E−03 ⊚ Zr 0.052 6.28E−06 1.22E−04 2.37E−03 ⊚ 0.0256.19E−06 1.25E−04 2.52E−03 ⊚ Al 0.155 5.18E−06 9.38E−05 1.70E−03 X Si0.150 4.49E−06 8.62E−05 1.66E−03 X None 0.000 6.32E−06 1.14E−04 2.07E−03X

TABLE 6 Seebeck Replace- Resis- Coeffi- Substituting ment tivity ρ cientα Power Judg- Metal M Ratio x (Ω · m) (V/° C.) Factor Pf ment Cu 0.0734.83E−06 −1.15E−04 2.74E−03 ⊚ 0.036 4.58E−06 −1.17E−04 3.00E−03 ⊚ 0.0074.64E−06 −1.14E−04 2.81E−03 ⊚ None 0.000 4.84E−06 −1.10E−04 2.51E−03 X

INDUSTRIAL APPLICABILITY

The rare earth-containing alloys in the present invention can be used asa thermoelectric conversion element for a thermoelectric conversionsystem.

The thermoelectric conversion system can be used as a waste heatrecovery system, a solar heat utilizing system, a co-generation system,and an automobile using the thermoelectric power generating device.

1. A process for producing a rare earth alloy comprising: heating a rawmaterial alloy to be a molten alloy, and quench-solidifying the moltenalloy, wherein the raw material alloy is compounded so as to have acomposition represented by the formula: RE_(x)(Co_(1-y)M_(y))₄Sb₁₂(wherein RE is at least either one member of La and Ce, M is at leastone member selected from the group consisting of Ti, Zr, Sn, Cu, Zn, Mnand Pb, 0<x≦1, and 0<y<1).
 2. The process for producing a rare earthalloy as set forth in claim 1, wherein the quench-solidifying isperformed at a rate more than 1×10²° C./sec.
 3. The process forproducing a rare earth alloy as set forth in claim 1, wherein thequench-solidifying is performed at a rate of 1×10² to 1×10³° C./sec. 4.The process for producing a rare earth alloy as set forth in claim 1,wherein the quench-solidifying during 1500 to 1700° C. is performed at arate of 1×10² to 1×10³° C./sec.
 5. The process for producing a rareearth alloy as set forth in claim 1, wherein the quench-solidifying isperformed by a strip casting method.
 6. The process for producing a rareearth alloy as set forth in claim 1, wherein the rare earth alloy is oneselected from the group consisting of a Heusler alloy, a half Heusleralloy, and a skutterudite alloy.